1. Field of the Invention
Embodiments of the present invention generally relate to the field of fluid extraction from bore holes. More particularly, the present invention relates to artificial lifting devices and methodologies for retrieving fluids, such as crude oil and other liquid hydrocarbons, from bores where the fluid does not have sufficient hydrostatic pressure to rise to the surface of the earth of its own accord.
2. Description of the Related Art
The recovery of fluids such as oil from bore holes is typically accomplished by the pumping of fluid collected in the bore hole by mechanical or fluid power means. These means are necessitated when the pressure of the fluid at the base of the bore hole does not exceed the hydrostatic head needed to cause the fluid to rise to, and over, the earths' surface of its own accord. Several methodologies are known to provide this pumping action, each with its own limitations.
In one methodology, a rod pump repeatedly reciprocates a rod up and down in the casing lining the well at the well head. The rod extends down the well to a production zone, where a pump is located and connected, at its outlet, to production tubing. As the pump downstrokes, the rod pushes a piston in the pump, to force fluids in the piston bore outwardly therefrom and thence into the production tubing. During rod upstroke, a valve closes the connection to the production tubing, and a second valve opens the piston bore to the formation, such that well fluid is drawn into the piston bore. Thus the recovery rate of fluid from the well is dependant upon the stroke of the rod and the number of strokes of the rod per unit of time. The pumps are typically used where the amount of oil to be recovered is marginal, but is sufficient to justify the relatively low cost of this pump arrangement.
A second methodology for artificial lifting uses a down hole positive displacement pump, typically a progressive cavity pump. These pumps typically use an offset helix screw configuration, where the threads of the screw or “rotor” portion are not equal to those of the stationary, or stator portion over the length of the pump, to effect a positive displacement of the fluid through the pump. This requires that the rotating surface of the rotor be sealingly engaged to that of the stator. This is typically accomplished by providing at least the inner bore surface of the stator with a compliant material such as neoprene rubber. The rotor pushes against this compliant material as the rotor rotates, thereby sealing the cavity formed between it and the stator to positively displace fluid through the pump. The rotor is driven by a rod extending down the casing from the surface, and this rod is rotated at relatively low rpm to cause pump operation. One problem associated with this methodology is that these pumps have limited applicability where high temperatures are encountered.
An additional downhole style of pump is the rotary pump, such as a vane or turbine pump, which uses a high speed rotation of an impeller(s) to accelerate fluids and direct them up the bore. Rotation of the impeller(s) is typically accomplished by coupling the impellers(s) to an electric motor which is attached to the impeller(s) downhole. Although it would be desirable to rotate the impeller(s) by a mechanical, surface mounted means, such as a surface mounted motor having a rotateable rod extending down the well bore, this is typically not done, because the speed at which the rod would have to be turned results in “whipping” or other imbalance effects of the rod, causing the relatively long rod to strike the casing or production tubing, eventually rupturing one or both of the rod, tubing and/or casing. Additionally, the durability of the electric motor in the hostile downhole location is limited, and as a result, the motors typically fail after nine months to one year, thereby requiring pulling of the string to retrieve and replace the motor.
A further method of well bore fluid recovery is known as jet pumping. This methodology takes advantage of the venturi effect, whereby the passage of fluid through a venturi causes a pressure drop, and the well fluids being recovered are thereby brought into the fluid stream. To accomplish this in a well, a hollow string is suspended in the casing to the recovery level, and the jet pump is located at the end of the tubing within the production zone of the well. The jet pump includes an inlet, a reduced diameter portion and a flared outlet, thereby forming a venturi. A passage extends between this venturi and the production zone. A fluid under pressure is flowed down the string and through the passages in the pump and thence up to the surface through the annulus between the well casing and the hollow string. The passing of the high pressure fluid through the venturi causes a pressure drop in the high pressure fluid, and thus in the passage to the production zone, thereby causing the production fluids to be pulled into the stream of high pressure fluid passing through the pump and thus carried to the surface therewith. Preferably, the fluid being used for recovery is of the same species as that being recovered. Thus, excess returns of fluid are recovered, and the remaining fluid is recycled and again directed down the well. This technique suffers from limited fluid recovery rate and the need for extensive equipment, the cost of which typically exceeds the value of the oil which may be recovered, which would be acceptable if the recovery rate were greater.
An additional method of well bore fluid recovery is gas-assisted lifting, in which a gas is injected into the fluid to be recovered. The injected gas forms bubbles in the fluid. These bubbles rise to the surface and propel well fluids upwardly therewith. This technique likewise suffers from limited fluid recovery and the need for extensive equipment, the cost of which typically exceeds the value of the oil which may be recovered.
Therefore, there exists in the art a need to provide enhanced artificial lifting methods, techniques and apparatus, having a greater return on investment and or durability.